Rod locking apparatus

ABSTRACT

A rod locking apparatus includes a housing which includes a first tubular passage and a second tubular passage which are arranged to intersect with each other, the first tubular passage including a serrated locking surface, and a wedge piston slidably arranged in the first tubular passage. The wedge piston includes a front side which includes a wedge surface which engages an end surface of a rod to be locked, and a serrated rear side which engages with the serrated locking surface.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. § 371 of International Application No. PCT/NO2016/050167, filed on Aug. 15, 2016 and which claims benefit to Great Britain Patent Application No. 1514762.2, filed on Aug. 19, 2015. The International Application was published in English on Feb. 23, 2017 as WO 2017/030444 A1 under PCT Article 21(2).

FIELD

The present invention relates to a rod locking apparatus, and in particular to a rod locking apparatus suitable for use in locking the actuators in ram-type blow out preventers.

BACKGROUND

The present invention relates to a rod locking device for locking reciprocating piston type fluid actuators in a preferred position. Actuators of this type are particularly suited for positioning the rams of ram-type blow out preventers. It is advantageous and desirable to mechanically lock the rods of these actuators to provide that the blow out preventer rams will be maintained in a preferred position should hydraulic pressure be lost.

Relevant prior art systems include U.S. Pat. No. 4,969,390 which describes a ram locking apparatus for blowout preventer rams which allows the rams to be locked in the closed position. A tapered end of a rod and a wedge surface of a piston have serrated surfaces to increase friction between the wedging surfaces and to provide a self-locking engagement in a small, compact apparatus.

Other related prior art includes U.S. Pat. No. 2,632,425, U.S. Pat. No. 3,050,943, U.S. Pat. No. 3,242,826, U.S. Pat. No. 3,918,478, U.S. Pat. No. 3,941,141, U.S. Pat. No. 4,188,860, U.S. Pat. No. 4,290,577, U.S. Pat. No. 4,305,565, U.S. Pat. No. 4,519,571, U.S. Pat. No. 4,601,232, U.S. Pat. No. 4,840,346, U.S. Pat. No. 4,969,627, U.S. Pat. No. 5,025,708, and U.S. Pat. No. 5,056,418.

SUMMARY

In an embodiment, the present invention provides a rod locking apparatus which includes a housing comprising a first tubular passage and a second tubular passage which are arranged to intersect with each other, the first tubular passage comprising a serrated locking surface, and a wedge piston slidably arranged in the first tubular passage. The wedge piston comprises a front side which comprises a wedge surface which is configured to engage an end surface of a rod to be locked, and a serrated rear side which is configured to engage with the serrated locking surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basis of embodiments and of the drawings in which:

FIG. 1 is a perspective view of a cross-section through an assembly of a rod locking apparatus according to the present invention and a tail rod of a blowout preventer actuator;

FIG. 2 is a longitudinal cross-section through the assembly illustrated in FIG. 1 in the open position;

FIG. 3 is a longitudinal cross-section through the assembly illustrated in FIG. 2 in the closed position;

FIG. 4 is a perspective view of the wedge piston and serrated rear side of the rod locking apparatus illustrated in FIG. 1; and

FIG. 5 is a perspective view of the serrated locking surface of the rod locking apparatus illustrated in FIG. 1.

DETAILED DESCRIPTION

In an embodiment, the present invention provides a rod locking apparatus comprising:

-   -   a housing having a first and second intersecting tubular         passages, the first tubular passage being provided with a         serrated locking surface; and     -   a wedge piston slidably arranged in the first tubular passage;     -   the wedge piston having a front side with a wedge surface         adapted in use to engage an end surface of a rod to be locked;     -   wherein, the wedge piston has a serrated rear side which engages         with the serrated locking surface.

Providing the rear side of the wedge piston with serrations which engage with the serrated locking surface means that the area of contact between the two serrated surfaces can be larger than in the arrangement described in U.S. Pat. No. 4,969,390. This provides a higher frictional locking force, and therefore provides more secure locking and/or allows a larger wedge angle to be used. A larger wedge angle allows for a shorter stroke length, and thus a shorter and more compact locking device.

The serrated locking surface may be integral with the remainder of the housing, or may be provided on a separate support part which is fixed relative to the housing.

The wedge piston is movable between a closed position in which it substantially blocks the second tubular passage, and an open position in which the second tubular passage is open.

The wedge piston may be provided with a through passage which extends from the front side to the rear side of the wedge piston generally parallel to the second tubular passage so that, when the wedge piston is in the open position, the through passage is generally coaxial with the second tubular passage, and when the wedge piston is in the closed position, the through passage is not aligned with the second tubular passage.

The rear side of the wedge piston may be inclined at an angle of between 10 and 20° to the wedge surface. In an embodiment, the rear side of the wedge piston can, for example, be inclined at an angle of around 12° to the wedge surface.

The first tubular passage may extend at an angle of between 100 and 110° to the second tubular passage. In an embodiment, the first tubular passage can, for example, extend at an angle of 102° to the second tubular passage.

The wedge piston may further be provided with two end surfaces which extend generally perpendicular to the rear side of the wedge piston.

A first one of the two end surfaces may provide a first piston face on which pressurized fluid introduced into a first end of the first tubular passage acts to push the wedge piston along the first tubular passage towards a second end thereof.

A second one of the two end surfaces may provide a second piston face on which pressurized fluid introduced into the second end of the first tubular passage acts to push the wedge piston along the first tubular passage towards the first end thereof.

Movement of the wedge piston from the open position to the closed position may comprise movement of the wedge piston from the second end of the first tubular passage towards the first end of the first tubular passage, and vice versa.

The surface area of the first piston face may be greater than the surface area of the second piston face.

The rod locking apparatus is further provided with a seal which extends between the housing and the wedge piston to substantially prevent a flow of fluid along the first tubular passage past the seal, while allowing the wedge piston to slide along the first tubular passage. The seal is advantageously mounted on the wedge piston. In an embodiment, the seal can, for example, comprise an O-ring mounted in a groove in the wedge piston.

The housing may further be provided with a first end cap which closes the first tubular passage at a first end thereof. The first end cap may be provided with an aperture and a pressurized fluid supply device which supplies a pressurized fluid into the first end of the first tubular passage via the aperture in the first end cap.

The housing may further be provided with a second end cap which closes the first tubular passage at a second end thereof. The second end cap may be provided with an aperture and a pressurized fluid supply device which supplies a pressurized fluid into the second end of the first tubular passage via the aperture in the end cap.

The housing may be provided with a supply tube which extends from the aperture in the second end cap into a bore in the wedge piston, there being a seal between the supply tube and the wedge piston which provides a substantially fluid tight seal between an interior surface of the wedge piston surrounding the bore and an exterior surface of the supply tube. In this case, an end portion of the bore is the second piston face.

In an embodiment, the present invention provides an assembly of a rod locking apparatus having a rod located in the second tubular passage, the rod having a first end which is located in the second tubular passage and a second end which extends out of the second tubular passage.

The surface area of the serrated locking surface is advantageously greater than the surface area of the first end of the rod.

In an embodiment, the present invention provides a rod locking apparatus comprising:

-   -   a housing having a first and second intersecting tubular         passages;     -   a wedge piston slidably arranged in the first tubular passage;     -   the wedge piston having a front side with a wedge surface         adapted in use to engage an end surface of a rod to be locked,         and two end surfaces which extend generally perpendicular to the         rear side of the wedge piston;     -   the wedge piston being movable between a closed position in         which it substantially blocks the second tubular passage, and an         open position in which the second tubular passage is open;     -   a first one of the two end surfaces providing a first piston         face on which a pressurized fluid introduced into a first end of         the first tubular passage acts to push the wedge piston along         the first tubular passage to a second end thereof; and     -   a second one of the two end surfaces providing a second piston         face on which pressurized fluid introduced into the second end         of the first tubular passage acts to push the wedge piston along         the first tubular passage to the first end thereof;     -   movement of the wedge piston from the open position to the         closed position comprising movement of the wedge piston from the         second end of the first tubular passage to the first end of the         first tubular passage, and vice versa,     -   wherein, the surface area of the first piston face is greater         than the surface area of the second piston face.

This advantageously allows for a reliable unlocking due to the higher force from the larger piston. A rod locking apparatus having a large interacting locking area may in particular have a large frictional locking force, and may thus need higher force to unlock.

The rod locking apparatus according to this embodiment may have any of the features or any combination of features of the rod locking apparatus according to the previously described embodiments.

In an embodiment, the present invention provides a new and improved subsea ram type blowout preventer which is a hydraulically actuated mechanical ram locking device. The device may be actuated as part of the single, overall rams closing function, or as a separate ram locking only function. The ram locking device is mounted as an integral sub-assembly to the pressure containing and controlling ram BOP bonnet assembly, whereby the bonnet assembly is mounted to the ram type BOP main pressure controlling and containing body member.

Blowout preventers were developed to cope with extreme erratic pressures and uncontrolled flow emanating from a well reservoir during drilling. Known as a “kick”, this flow of pressure can lead to a potentially catastrophic event called a “blowout”. In addition to controlling the downhole well pressure and the flow of oil and gas, blowout preventers are intended to prevent tubular goods used in well drilling, such as, drill pipe, casing, collars, tools and drilling fluid, from being blown out of the wellbore when a kick or blowout threatens. Blowout preventers are critical to the safety of the crew, the drilling rig, the environment, and to the monitoring and maintenance of well integrity; blowout preventers are thus intended to provide an additional and fail-safe barrier to the systems that include them.

Ram-type blowout preventers are part of an overall pressure control system used in oil and gas operations commonly used as pressure containment and unexpected wellbore pressure spikes and well pressure control events. A conventional ram-type BOP is similar in operation to a gate valve, but uses a pair of opposing steel plungers or rams. The rams extend toward the center of the wellbore to restrict flow or retract open in order to permit flow. The inner and top faces of the rams are fitted with composite steel and elastomeric packers that press against each other, against the wellbore, and around well tubular members running through the wellbore. Outlets at the sides of the BOP housing (body) are used for connection to choke and kill lines or valves.

Rams, or ram blocks, are generally of five common types: pipe, variable bore pipe, blind, shear, and blind shear. The ram type blow out preventer is further usually integrated with additional well containment and control devices that inclusively make up a subsea blowout preventer stack.

FIG. 1 illustrates an embodiment of a rod locking device 100 according to the present invention. The rod locking device 100 comprises a main housing 1 having a first tubular passage 22 and a second tubular passage 23. In this embodiment, the main housing 1 is provided with a mounting attachment 5 to attach the rod locking device 100 to the BOP bonnet 20, as illustrated in FIG. 2. The first tubular passage 22 is provided with a serrated locking surface 4 a, which in this embodiment is provided on a support part 4 (illustrated in detail in FIG. 5), which is fixed relative to the main housing 1 and which is described in further detail below. It should be appreciated, however, that the support part 4 may be integral with the main housing 1.

A wedge piston 12 is slidably provided in the main housing 1. The wedge piston 12 has a front side with a wedge surface 11 which engages a back end surface 13 a of a tail rod 13 of a blowout preventer actuator. The wedge piston 12 also has a serrated rear side which engages with the serrated locking surface 4 a.

The tail rod 13 is coupled to a hydraulic, ram operating piston 14 provided in the BOP bonnet 20 (see FIG. 2), and extends into the second tubular passage 23. The wedge piston 12 is movable between a closed position in which it substantially blocks the second tubular passage 23 and an open position in which the second tubular passage 23 is open.

In this embodiment, the wedge piston 12 has a transverse bore forming a through passage 17 which extends from the front side to the rear side of the wedge piston 12 generally parallel to the second tubular passage 23 and, when the wedge piston 12 is in the open position, is aligned with the second tubular passage 23 so that the tail rod 13 may extend along the second tubular passage 23, as shown in FIG. 2. When the wedge piston 12 is in the closed position, the through passage 17 is not aligned with the second tubular passage 23, as illustrated in FIG. 1.

The wedge piston 12 incorporates a spline shaped serrated rear side 16 which utilize a series of ridges, or teeth, that mesh with grooves in the serrated locking surface 4 a (see FIG. 5). The design of the serrations on the serrated rear side 16 of the wedge piston 12 and the serrated locking surface 4 a may be according to one of the alternatives described in U.S. Pat. No. 4,969,390 or any other suitable design. This may include splines, grooves, ridges, or teeth, or a combination thereof, suitable for producing a mating motion and a friction-based locking effect between the serrated rear side 16 of the wedge piston 12 and the serrated locking surface 4 a.

The serrated rear side 16 of the wedge piston 12 is inclined at an angle of between 10 and 20° to the wedge surface 11. In this embodiment, the serrated rear side 16 of the wedge piston 12 is inclined at an angle of around 12° to the wedge surface 11. The first tubular passage 22 extends at an angle of between 100 and 110° to the second tubular passage 23. In this embodiment, the first tubular passage 22 extends at an angle of 102° to the second tubular passage 23. Designing the first tubular passage 22 to extend at an angle to the second tubular passage 23 which corresponds to the angle of inclination between the serrated rear side 16 of the wedge piston 12 and the wedge surface 11 permits the back end surface 13 a of the tail rod 13 to extend perpendicularly to the rod longitudinal axis. Other combinations of inclination angle and angle between the first tubular passage 22 and the second tubular passage 23 are, however, possible.

The wedge piston 12 is further provided with two end surfaces 9, 24 which extend generally perpendicular to the serrated rear side 16 of the wedge piston 12. A first end surface 9 of the two end surfaces 9, 24 provides a first piston face on which pressurized fluid introduced into a first end 27 a of the first tubular passage 22 acts to push the wedge piston 12 along the first tubular passage 22 towards a second end 27 b thereof. A second end surface 24 of the two end surfaces 9, 24 provides a second piston face on which pressurized fluid introduced into the second end 27 b of the first tubular passage 22 acts to push the wedge piston along the first tubular passage 22 towards the first end 27 a thereof.

In this embodiment, movement of the wedge piston 12 from the open position to the closed position comprises a translational movement of the wedge piston 12 in a direction extending from the second end 27 b of the first tubular passage 22 towards the first end 27 a of the first tubular passage 22, and vice versa.

A first end cap 8 a and a second end cap 8 b close the first tubular passage 22 at the first end 27 a and second end 27 b, respectively. Apertures in the form of channels 21 a and 21 b are provided through the first end cap 8 a and the second end cap 8 b along with a device for supplying pressurized fluid therethrough and into the first tubular passage 22. The rod locking device 100 is provided with a seal 26 which extends between the main housing 1 and the wedge piston 12 to substantially prevent the flow of fluid along the first tubular passage 22 past the seal 26, while allowing the wedge piston 12 to slide along the first tubular passage 22. In this embodiment, the seal 26 is provided in the form of an O-ring mounted in a groove on the wedge piston 12, to seal against the inner surface of the first tubular passage 22 and delimit a cavity 15. Providing pressurized fluid through channel 21 a and into cavity 15 produces a pressure force on the first end surface 9 of the wedge piston 12 and acts to push the wedge piston 12 along the first tubular passage 22 in a direction away from the first end 27 a. This moves the wedge piston 12 into the open, or unlocked, position of the rod locking device 100 and BOP ram.

In this embodiment, from the second end cap 8 b, a supply tube 2 extends into the first tubular passage 22 and into a wedge piston bore 10 provided in the wedge piston 12. The supply tube 2 has an internal bore permitting hydraulic fluid communication from a hydraulic fluid supply (not shown in the drawings) through aperture/channel 21 b in the second end cap 8 b and into wedge piston bore 10. The supply tube 2 is sealed against wedge piston bore 10, for example, by O-rings 25 (see FIGS. 2 and 3). The second piston face 24 is therefore formed by the end face of the wedge piston bore 10. Provision of hydraulic fluid pressure into wedge piston bore 10 through supply tube 2 generates a pressure force on the second piston face 24 in the wedge piston bore 10 and urges the wedge piston 12 away from second end 27 b along the first tubular passage 22 and to a locked position of the rod locking device 100 and BOP ram.

As a result of using a wedge piston bore 10 and supply tube 2, it will be appreciated that, in this embodiment of the present invention, the surface area of the first piston face 9 is greater than the surface area of the second piston face 24. This means that, for a given fluid pressure, the force moving the wedge piston 12 to the open position is greater than the force moving the wedge piston 12 to the closed position. This may have the advantage of allowing a reliable unlocking of the rod locking device 100 and consequent opening of the BOP.

This need not be the case, however, and in an alternative embodiment of the present invention, the second piston face 24 may be provided on the end of the wedge piston 12 facing the second end 27 b of the first tubular passage 22, the second piston face 24 of the wedge piston 12 being sealed against the inner surface of the first tubular passage 22, in a similar way to the arrangement provided by first piston face 9. Referring now to FIG. 2, a rod locking device 100 is shown in an open, or unlocked, position. The BOP ram is open in this state. The rod locking device 100 is fixed to a BOP bonnet 20 by mounting attachment 5. A ram operating piston 14 is provided in the BOP bonnet 20 to operate the ram. In this position, the through passage 17 of the wedge piston 12 is aligned with the second tubular passage 23 and the tail rod 13 extends through the through passage 17.

FIG. 3 shows the closed position of the rod locking device 100. In this state, closing of the BOP ram has been performed by ram operating piston 14 and the tail rod 13 has been moved out of the through passage 17. Subsequently, fluid pressure is provided through channel 21 b and into wedge piston bore 10 to move the wedge piston 12 towards the first end 27 a. As the wedge piston approaches its end position towards the first end 27 a, the wedge surface 11 engages the back end surface 13 a of the tail rod 13. The serrated rear side 16 of the wedge piston 12 is inclined by approximately 12° to the wedge surface 11, thus moving the wedge piston 12 towards the first end 27 a produces a wedging force between the wedge piston 12 and the back end surface 13 a and support part 4. This produces a mating motion between the serrated rear side 16 of the wedge piston 12 and the serrated locking surface 4 a (see FIG. 5), which provides a friction-based self-locking effect. Even in the case of loss of fluid pressure in wedge piston bore 10 and a back force acting by the tail rod 13 on the wedge surface 11, the friction between the serrated rear side 16 of the wedge piston 12 and the serrated locking surface 4 a will thus keep the wedge piston 12 in the locked position.

To open the rod locking device 100, fluid pressure is provided through channel 21 a to act on first piston surface 9 as described above. Advantageously, as first piston surface 9 is provided with a larger area than second piston face 24′ (see FIG. 1), the rod locking device 100 can be securely unlocked even in the case of a strong friction locking effect.

FIG. 4 shows details of the wedge piston 12 with the serrated rear side 16 and the through passage 17. FIG. 4 further shows the support part 4. The support part 4 may have a throughbore 27 which is aligned with the second tubular passage 23 (see FIG. 1) to allow the tail rod 13 to extend through the throughbore 27 in the open position of the ram locking device 100, as shown in FIG. 2. FIG. 4 shows further details of a part of the support part 4, showing the serrated locking surface 4 a which, in use, engages with the serrated rear side 16 of the wedge piston 12.

Advantageously, the serrated rear side 16 is provided along substantially the full length of the wedge piston 12. The area of the serrated locking surface 4 a may be adapted for a particular use or operating requirements, thus providing freedom to, for example, use a large locking surface in applications with high safety requirements.

The rod locking device according to the present invention thus provides a simple, robust, and more reliable, hydraulically actuated, mechanical assembly that provides a way to lock the rams of a ram-type blowout preventer in the closed and sealed position, even if hydraulic pressure is lost or removed, and only allows the rams to open when hydraulic pressure is intentionally applied to the BOP and locking mechanism's operating system for the expressed purpose of opening the blowout preventer's ram assemblies.

The rod locking device according to the present invention is suitable to lock any type of ram (pipe, variable bore pipe, shear, blind, shearing blind) in an infinite range of closed positions, providing a ridged mechanical locking mechanism for rams that will not allow them to open, or retreat from their closed position, even if no closing pressure is applied, or maintained. The rod locking device is equally suited for use with wellbore control devices utilizing gates, including such gates having shearing capability.

When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilized for realizing the present invention in diverse forms thereof.

The present invention is not limited to embodiments described herein; reference should be had to the appended claims. 

What is claimed is: 1-27. (canceled)
 28. A rod locking apparatus comprising: a housing comprising a first tubular passage and a second tubular passage which are arranged to intersect with each other, the first tubular passage comprising a serrated locking surface; and a wedge piston slidably arranged in the first tubular passage, the wedge piston comprising a front side which comprises a wedge surface which is configured to engage an end surface of a rod to be locked, and a serrated rear side which is configured to engage with the serrated locking surface.
 29. The rod locking apparatus as recited in claim 28, wherein, the serrated locking surface is arranged to be integral with the housing, or the serrated locking surface is arranged on a separate support part which is fixed relative to the housing.
 30. The rod locking apparatus as recited in claim 28, wherein the serrated rear side of the wedge piston is inclined at an angle of between 10 and 20° relative to the wedge surface.
 31. The rod locking apparatus as recited in claim 28, wherein the first tubular passage extends at an angle of between 100 and 110° relative to the second tubular passage.
 32. The rod locking apparatus as recited in claim 28, wherein the wedge piston is movable between a closed position in which the wedge piston substantially blocks the second tubular passage, and an open position in which the second tubular passage is open.
 33. The rod locking apparatus as recited in claim 32, wherein the wedge piston further comprises a through passage which is arranged to extend from the front side to the serrated rear side of the wedge piston generally parallel to the second tubular passage so that, when the wedge piston is in the open position, the through passage is generally coaxial with the second tubular passage, and when the wedge piston is in the closed position, the through passage is not aligned with the second tubular passage.
 34. The rod locking apparatus as recited in claim 32, wherein the wedge piston further comprises two end surfaces which extend generally perpendicular to the serrated rear side of the wedge piston.
 35. The rod locking apparatus as recited in claim 34, wherein, the two end surfaces comprise a first end surface, the first tubular passage further comprises a first end and a second end, and the first end surface comprises a first piston face on which a pressurized fluid introduced into the first end of the first tubular passage acts to push the wedge piston along the first tubular passage towards the second end of the first tubular passage.
 36. The rod locking apparatus as recited in claim 35, wherein, the two end surfaces further comprise a second end surface, and the second end surface comprises a second piston face on which a pressurized fluid introduced into the second end of the first tubular passage acts to push the wedge piston along the first tubular passage towards the first end of the first tubular passage.
 37. The rod locking apparatus as recited in claim 36, wherein, a movement of the wedge piston from the open position to the closed position comprises a movement of the wedge piston from the second end of the first tubular passage towards the first end of the first tubular passage, and a movement of the wedge piston from the first end of the first tubular passage towards the second end of the first tubular passage.
 38. The rod locking apparatus as recited in claim 36, wherein, the first piston face comprises a first piston face surface area, the second piston face comprises a second piston face surface area, and the first piston face surface area is greater than the second piston face surface area.
 39. The rod locking apparatus as recited in claim 35, wherein the housing further comprise a first end cap which is configured to close the first tubular passage at the first end.
 40. The rod locking apparatus as recited in claim 39, wherein the first end cap comprises an aperture and a pressurized fluid supply device configured to supply a pressurized fluid into the first end of the first tubular passage via the aperture in the first end cap.
 41. The rod locking apparatus as recited in claim 40, wherein the housing further comprises a second end cap which is configured to close the first tubular passage at the second end.
 42. The rod locking apparatus as recited in claim 41, wherein the second end cap comprises an aperture and a pressurized fluid supply device configured to supply a pressurized fluid into the second end of the first tubular passage via the aperture in the second end cap.
 43. The rod locking apparatus as recited in claim 42, wherein, the wedge piston further comprises a bore, and the housing further comprises a supply tube which extends from the aperture in the second end cap into the bore in the wedge piston, the rod locking apparatus further comprising: a seal arranged between the supply tube and the wedge piston, the seal being configured to provide a substantially fluid tight seal between an interior surface of the wedge piston surrounding the bore and an exterior surface of the supply tube.
 44. An assembly comprising: the rod locking apparatus as recited in claim 28; and a rod arranged in the second tubular passage, the rod comprising a rod first end which is arranged in the second tubular passage and a rod second end which is arranged to extend out of the second tubular passage.
 45. The assembly as recited in claim 44, wherein, the rod first end comprises a rod first end surface area, the serrated locking surface comprises a serrated locking surface area, and the serrated locking surface area is greater than the rod first end surface area.
 46. A rod locking apparatus comprising: a housing comprising a first tubular passage and a second tubular passage which are arranged to intersect with each other, the first tubular passage comprising a first end and a second end; and a wedge piston slidably arranged in the first tubular passage, the wedge piston comprising a front side which comprises a wedge surface which is configured to engage an end surface of a rod to be locked, a rear side, and a first end surface and a second end surface which each extend generally perpendicular to the rear side of the wedge piston, the wedge piston being movable between a closed position in which the wedge piston substantially blocks the second tubular passage, and an open position in which the second tubular passage is open, wherein, the first end surface comprises a first piston face on which a pressurized fluid introduced into the first end of the first tubular passage acts to push the wedge piston along the first tubular passage to the second end of the first tubular passage, the second end surface comprises a second piston face on which a pressurized fluid introduced into the second end of the first tubular passage acts to push the wedge piston along the first tubular passage to the second end of the first tubular passage, a movement of the wedge piston from the open position to the closed position comprises a movement of the wedge piston from the second end of the first tubular passage to the first end of the first tubular passage, and vice versa, and a surface area of the first piston face is greater than a surface area of the second piston face. 